vue3.0 watch监听

vue2.x watch

<template>
  <h2>求和：{{ sum }}</h2>
  <button @click="sum++">++</button>
</template>

<script>
import { ref } from "vue";
export default {
  // vue2.x 简易写法
  watch: {
    sum(newval, oldval) {
      console.log(newval, oldval);
    },
  },
  setup() {
    const sum = ref(0);
    return {
      sum,
    };
  },
};
</script>

正常打印，说明vue3中也可以使用vue2.x的写法

完整写法就是带有配置项的

<template>
  <h2>求和：{{ sum }}</h2>
  <button @click="sum++">++</button>
</template>

<script>
import { ref } from "vue";
export default {
  // vue2.x 简易写法
  // watch: {
  //   sum(newval, oldval) {
  //     console.log(newval, oldval);
  //   },
  // },
  watch: {
    sum: {
      immediate:true, // 立即执行一次
      deep:true,// 深度监听
      handler(ewval, oldval) {
        console.log(newval, oldval);
      },
    },
  },
  setup() {
    const sum = ref(0);
    return {
      sum,
    };
  },
};
</script>

vue3.0 watch
vue3中的watch是一个函数，所以需要单独引入

<template>
  <h2>求和：{{ sum }}</h2>
  <button @click="sum++">++</button>
</template>

<script>
import { ref, watch } from "vue";
export default {
  setup() {
    const sum = ref(0);
    // 是一种行为 所以没有返回
    watch(sum, (newval, oldval) => {
      console.log("vue3.0", newval, oldval);  
    });
    return {
      sum,
    };
  },
};
</script>

以上演示了监听单个ref响应式数据，现在演示监听多个，比较简单的写法就是用两个watch

<template>
  <h2>求和：{{ sum }}</h2>
  <button @click="sum++">++</button>
  <hr />
  <h2>招呼：{{ info }}</h2>
  <button @click="info += '!'">打招呼</button>
</template>

<script>
import { ref, watch } from "vue";
export default {
  setup() {
    const sum = ref(0);
    const info = ref("hello");
    // 1.监听ref单个响应式数据
    watch(sum, (newval, oldval) => {
      console.log("求和", newval, oldval);
    });
    // 2.监听多个响应式数据 在vue2.x中watch是个配置项，所以只能写一个watch，vue3.0中是函数，可以写多个
    watch(info, (newval, oldval) => {
      console.log("招呼：", newval, oldval);
    });
    return {
      sum,
      info,
    };
  },
};
</script>

<template>
  <h2>求和：{{ sum }}</h2>
  <button @click="sum++">++</button>
  <hr />
  <h2>招呼：{{ info }}</h2>
  <button @click="info += '!'">打招呼</button>
</template>

<script>
import { ref, watch } from "vue";
export default {
  setup() {
    const sum = ref(0);
    const info = ref("hello");
    // 1.监听ref单个响应式数据
    // watch(sum, (newval, oldval) => {
    //   console.log("求和", newval, oldval);
    // });
    // 2.监听多个响应式数据 在vue2.x中watch是个配置项，所以只能写一个watch，vue3.0中是函数，可以写多个
    watch([sum, info], (newval, oldval) => {
      console.log("新值newval", newval);
      console.log("旧值oldval", oldval);
    });
    return {
      sum,
      info,
    };
  },
};
</script>

immediate，deep配置如下，

<template>
  <h2>求和：{{ sum }}</h2>
  <button @click="sum++">++</button>
  <hr />
  <h2>招呼：{{ info }}</h2>
  <button @click="info += '!'">打招呼</button>
</template>

<script>
import { ref, watch } from "vue";
export default {
  setup() {
    const sum = ref(0);
    const info = ref("hello");
    // 1.监听ref单个响应式数据
    watch(
      // 第一个参数，监视的数据
      sum,
      // 第二个参数，监视的回调
      (newval, oldval) => {
        console.log("求和", newval, oldval);
      },
      // 第三个参数，监视的配置
      { immediate: true}
    );
    // 2.监听多个响应式数据 在vue2.x中watch是个配置项，所以只能写一个watch，vue3.0中是函数，可以写多个
    // watch([sum, info], (newval, oldval) => {
    //   console.log("新值newval", newval);
    //   console.log("旧值oldval", oldval);
    // });
    return {
      sum,
      info,
    };
  },
};
</script>

标签：console,sum,watch,newval,oldval,vue3.0,ref,监听
来源： https://blog.csdn.net/weixin_45780818/article/details/119190963